The manufacturing methods and apparatuses for membrane mobile polymer microfluidic chip are the key for microfluidics technology to realize industrial production and enter into application market. By using the laser radiation fusion welding method to weld polymer, the precision and quality of welding can be improved and the micro-welding processing can be carried out.
The Chinese invention patent ZL00101924.4 “Laser welding method and apparatus for welding plastic workpieces or welding plastics and other materials” discloses a method for using laser to weld plastic workpieces; whereby the two workpieces to be welded are pressed together, the weld faces thereof contact with each other, the workpiece close to laser is transparent to the laser, the other workpiece is not transparent and used to absorb the heat generated by the laser, and the welding is realized through application of laser; the Chinese invention patent ZL 03132664.1 “Method and apparatus used to process workpieces” discloses a fixing method and apparatus for using laser to weld and process workpieces; wherein the apparatus is composed of upper clamping component and lower clamping component, the upper clamping component mainly consists a transparent upper clamping plate and a transparent elastic membrane; the lower clamping component consists a lower clamping plate, a pressure chamber and a pressure piston; the welding laser is eradiated from above, and the control on welding area is realized through the transparent area and non-transparent area of a mask placed on the transparent upper clamping plate; the weld faces of two workpieces contact with each other under pressure, the upper workpiece which is close to laser source shall be transparent to laser, and the lower workpiece shall be able to absorb the laser as much as possible. This method and apparatus are applicable to the welding of two workpieces which are rigid or elastic materials without considering deformation.
As for the workpieces to be welded in a manufacturing process of membrane mobile polymer microfluidic chip, one is a transparent elastic membrane, and the other is a non-transparent rigid substrate. In the course of welding, two weld faces shall be flat and in contact with each other, and vertical pressure must exist; in practice, the weld face of substrate to be welded is not an ideal plane, but is rugged. A flat plate is adopted as the upper clamping plate, but even under the pressure, there still exist clearance and gas film in the plane, so that the welding can't be realized; a transparent elastic pad is added under the flat plate, so as to make some compensation for planeness. Since the operating principle is based on the elastic deformation of elastic pad under the pressure, the deformation at raised portion of substrate is larger under the action of higher pressure, and the deformation at depressed portion under the action of lower pressure. As a result, after the fusion welding, the welding effect varies in different portions; at depressed portion, the situation that the welding is not firm or no welding is realized may occur; abrupt change exists at the edge of groove on substrate, the membrane is not supported, and the pressure generates a tensile force to the membrane and directly affects the flatness of membrane after welding; as for a precision membrane welding such as microfluidics, the welding is not qualified; if the transparent elastic pad is thickened and hardened, it can ensure the relatively large elastic deformation and avoid the excessive deformation at the structure such as groove, but the thickened transparent pad may absorb the laser and thus affect the welding.
Therefore, the existing technologies can't realize a firm welding between substrate and membrane of microfluidic chip.